Definition from Wiktionary, the free dictionary
comet (plural comets)
- (astronomy) A celestial body consisting mainly of ice, dust and gas in a (usually very eccentric) orbit around the Sun and having a "tail" of matter blown back from it by the solar wind as it approaches the Sun.
- A celestial phenomenon with the appearance given by the orbiting celestial body.
Derived terms 
Related terms 
a celestial body, generally with a tail
- Third-person singular present indicative form of cometre.
- Second-person singular imperative form of cometre.
- third-person singular future active indicative of cōmō